Chart A-3 Dwell Fixed Over 50 Degrees

Chart A-3:

Wiring Diagram - Mixture Control Solenoid Dwell:

CHART A-3

DWELL FIXED OVER 50 DEGREES (RICH EXHAUST INDICATED)


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Determines whether problem is related to engine or electronics. The normal response would be dwell decreases (rich command), indicating that electronics, 02 sensor, harness, and ECM are OK, and fault is a rich engine condition. This may require a large air leak, if engine is very rich. When the mixture is lean enough, the engine will start to run rough.

2. Checks ECM response to a "lean" 02 signal. The normal response would be low dwell (rich command). No dwell change indicates a faulty ECM. Fault couldn't be an open wire because that would cause "Open Loop" operation and may set Code 13.


3. Checks for excessive voltage in 02 line. If under .55 volt, wire and ECM are OK and the fault is in 02 sensor, which could be the result of silicon contamination. If over .55 volt, wire is shorted to B+, or the ECM is faulty.

4. If plugging the PCV, or bowl vent vacuum hose, causes the dwell to decrease, that hose leads to the source of the problem.